This invention relates to the connection of one rigid tube such as a hollow drill stem to another by means of a threaded nipple or coupling. Assemblies of a string of connected drill stems or tubes of this kind are commonly used in circumstances where the task of adding to the drill string to increase its length is difficult and where it is desirable to ensure that the connection, once made is not accidentally negated.
It is often convenient where drill tubes are concerned to provide a joint which is suitable for transmitting axial as well as torsional loads without increasing the external diameter of the tubes at the joint, while still providing for a core to be extracted, if so desired, within the string of tubes.
United Kingdom Pat. Nos. 1,137,310 and 1,265,715 describe joints which meet the above-mentioned objectives but also entail certain disadvantages. Pat. No. 1,265,715 discloses one rod screwed into the end of another to form the joint. This join requires special forging of the male section and there is no disclosure of any means to prevent the rods from unscrewing when the drill string is rotated. In Pat. No. 1,137,310 a tapering male/female joint is swaged and brazed along the interface. The tubes are of different malleability. However, this process will not give a rigid joint suitable for the transmission of large torsional forces. In addition, the taper of the interface will reduce the resistance of the joint to axial forces tending to pull the tubes apart. Neither of these patents disclose the use of a connector or nipple.
It is an object of the invention to overcome or mitigate the above problems.